Re: Topband: FCP vs Gull Wing Elevated Radials
Hi Jerry, 65% is in the wheelhouse for DOG VF's. 400 to 600 ohms seems high. In the 12 county area around Raleigh/Durham/Chapel Hill, we measured 120 - 200 ohms resonant R. The variation you experienced, and also high R readings could be explained by a few nicks in the wire insulation toward the ends, which could have been there to start with, or perhaps you experienced critter nibble, or perhaps the ends were inadequately insulated from ground contact or the elements. DOG conductor in contact with ground moisture near the ends could completely skewer results. That's an electrical 1/4 wave between center and either end of the DOG. Inadvertently grounding an end will be transformed around the surge impedance of the wire to a quite higher impedance at center. An inadvertent partial grounding near the ends along with variation in ground surface moisture would explain erratic observations of high R and no resonance. 73 & Good Luck, Guy K2AV On Fri, Jul 26, 2019 at 10:34 PM K4SAV wrote: > K2AV said: > "Measured resonance of a fixed length gave us velocity factor (VF) and > other data. VF's based on those measurements ranged from 45% to 85%. > That huge variability certainly explained the BOG experience, and > suggested a solution, but that's another subject." > > > When I did those tests at my house the velocity factor of a dipole on > the ground was usually about 65% but many times there was no resonance > at all, so no way to calculate velocity factor. Total impedance was > usually 400 to 600 ohms but resistance and reactance were all over the > place. That dipole was tested on the ground at various times over a one > month period and never moved. I can only guess that must have been due > to variations in ground moisture content. > > I was also trying to use that data to help explain BOG performance, but > I didn't have much success. > > Jerry, K4SAV > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FCP vs Gull Wing Elevated Radials
K2AV said: "Measured resonance of a fixed length gave us velocity factor (VF) and other data. VF's based on those measurements ranged from 45% to 85%. That huge variability certainly explained the BOG experience, and suggested a solution, but that's another subject." When I did those tests at my house the velocity factor of a dipole on the ground was usually about 65% but many times there was no resonance at all, so no way to calculate velocity factor. Total impedance was usually 400 to 600 ohms but resistance and reactance were all over the place. That dipole was tested on the ground at various times over a one month period and never moved. I can only guess that must have been due to variations in ground moisture content. I was also trying to use that data to help explain BOG performance, but I didn't have much success. Jerry, K4SAV _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FCP vs Gull Wing Elevated Radials
Hi Wes, Thanks for posting up the Severns material. I had started looking for that, but without memory of exact words (which makes searching difficult), and without absolute certainty that Rudy was who I heard it from. You likely saved me an entire working day. If you're ever in the area, that's worth free pizza and beer and a no-cost friendly guest bedroom accommodation instead of a motel. Rudy's contention: "Confirmation of the NEC predictions was very satisfying but that work must not be taken uncritically! My articles on that work failed to emphasize how prone to asymmetric radial currents and degraded performance the 4-radial elevated system is. You cannot just throw up any four radials and get the expected results." ... is oddly separately confirmed by research done by a group of hams in the North Carolina Triangle area back in 2009. The task was to get an edge on the highly erratic success/failure of BOG's. We were examining velocity factor variation in an insulated dipole on ground (DOG) at various points in our region. The DOG was 151 ft or 47m, picked for round numbers in length and a probable resonance in or near 160 meters accounting for VF. Measured resonance of a fixed length gave us velocity factor (VF) and other data. VF's based on those measurements ranged from 45% to 85%. That huge variability certainly explained the BOG experience, and suggested a solution, but that's another subject. To underscore Rudy's assertion that local in-ground and other influence can screw up four raised 1/4 wave radials, I offer the DOG VF's, highly variable in different spots across the region, and in cases highly variable on the same property. The latter included a few where rotating the DOG 90 degrees about its center produced different VF's, varying 20% in one case. This was accompanied by the owner's assertion that there was nothing buried out there he knew about (pipes, electrical or phone feed, etc) and there had never been a septic field. One feature of this area is veins of sand, like fingers, near the surface bounded by hard-pan clay. One of these, with its water content, would have a considerably different effect if a wire ran across it, than if the wire ran parallel. And it would detune a BOG specifically tuned to the ground underneath, if the water table dropped and the sand finger drained out. So to a lesser degree, but still with effect, similarly oriented 4 x 1/4 wave elevated radials (over that exact spot exposed by the DOG) will have dissimilar resonances, and the old practice of resonating a PAIR or radials still would not deal if the variable situation was all under just one of the radials. The radials would have to be resonated individually with a single-ended test, largely unfamiliar and requiring a made up testing adapter and a graphing analyst that can display proper sign of reactance. Even after that, there still could be differences in ground induction which could not be adjusted out, causing differing R across the radials even after X was adjusted to zero. There is a certain amount of net RF field at ground that is minimized by a "pure" 4 x 1/4 system. However, if the radials vary in X and/or R, then the individual field phases at ground shift, and the net RF field under the radials increases, increasing ground losses. The resulting reactance at feed can introduce losses on common ferrite blocking devices. Blocking device and common mode losses can be reduced or eliminated by an Isolation Transformer, but the ground losses remain. This is NOT to say don't do it, but if all the potential loss factors for various counterpoises are considered on a particular ham's property, then an informed choice can at least optimize to the degree possible. But by all means put something up and get on the air. To the degree I can tell, ON4UN's 4 x 1/8 wave elevated radials will always beat out 4 x 1/4 elevated. At the same height and over the same center, the 4 x 1/8 must have only 1/5 the counterpoise ground power loss in watts of 4 x 1/4. Just be sure to use an isolation transformer with the 4 x 1/8 so you can use that coil to center the SWR (what everyone does anyway) without the penalty of common mode and blocking device loss. Connect the radial center point to the "FCP" connection on an isolation transformer. The 1/8 wave is not a resonance point or magic length like 1/4 wave. 1/8 wave-ish will always have some degree of reactance. One can make them uniformly a little shorter to deal with mounting points and keep all the radial ends in the clear. You just need a little more coil to resonate the whole thing. To agree with Wes, gull wings do have an immutable specific loss issue, which ought to discourage their use. The loss requires technical explanation, comparative modeling and illustrations to clarify the issue. The short answer is don't use gull wings, and the long answer I will have to post on k2av.com in a new section, when I can get to it. 73, Guy K2AV On Thu, Jul 25, 2019 at
Re: Topband: FCP vs Gull Wing Elevated Radials
I am going to add what may be a meaningless post to this thread. I live on a 1/4 acre lot in the black hole of San Jose California. Until very recently I was using a base loaded 1/8 wave vertical for 10 years. The vertical is on the side of the house 10 feet from the property line. I run eight 1/4 wave radials from the base of the vertical 48 inches high to the roof at about 10 feet where they make a 90° bend and run in various directions. The radial system forms a U shape. The system is highly asymmetrical and far from optimum. I run legal limit. This system has allowed me to work in excess of 150 countries on topband. The point I’m making is a dedicated top and operator can have what I would consider a high degree of success with even a compromise in antenna system. Don’t lot perfect, or even good, be the enemy of the best you can do. You might be surprised at what you can accomplish. 73, Bob AA6VB Robert L. Chortek _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FCP vs Gull Wing Elevated Radials
I guess I should have added "useful to me." At my location, I wouldn't dream of having elevated radials less than 6 feet above ground. Running them through the cactus and bushes could be just as difficult as on the ground, especially when they need to be considerably longer. There also needs to be a common-mode choke and lightning protection is more difficult and there are some mechanical issues. I'm going to liberally quote from another of Rudy's papers: https://rudys.typepad.com/files/qex-mar-apr-2012-1.pdf "Among amateurs there's been a long running discussion regarding the effectiveness of a vertical with an elevated ground system compared to one using a large number of radials either buried or lying on the ground surface. NEC modeling has indicated that an antenna with four elevated λ/4-radials would be as efficient as one with 60 or more λ/4 ground based radials. Over the years there have been a number of attempts to confirm or refute the NEC prediction experimentally with mixed results. These conflicting results prompted me to conduct a series of experiments directly comparing verticals with the two types of ground systems. The results of my experiments were reported in a series of QEX[1-7] and QST[8] articles (.pdf files of these articles are posted at: www.antennasbyn6lf.com ). From these experiments I concluded that at least under ideal conditions four elevated λ/4 radials could be equivalent to a large number of radials on the ground. Confirmation of the NEC predictions was very satisfying but that work must not be taken uncritically! My articles on that work failed to emphasize how prone to asymmetric radial currents and degraded performance the 4-radial elevated system is. You cannot just throw up any four radials and get the expected results. I'm by no means the first to point out that the performance of a vertical with only a few radials is sensitive to even modest asymmetries in the radial fan[10,11, 12], the presence of nearby conductors or even variations in the soil under the fan[9]. These can cause significant changes in the resonant frequency, the feedpoint impedance, the radiation pattern and radiation efficiency. These problems have been pointed out before but as far as I can tell no detailed follow-up has been published. Besides the practical problem of construction asymmetries, at many QTH's it's simply not possible to build an ideal elevated system even if you wanted to. There may not be enough space or there may be obstacles preventing the placement of radials in some areas or other limitations. I think it's very possible that some of the conflicting results from earlier experiments may well have been due to pattern distortion and increased ground loss that the simple 4-wire elevated system is susceptible to. As the sensitivity of the 4-radial system and it's consequences sunk into my consciousness I began to strongly recommend that people use at least 10-12 or more radials in elevated systems." Based on the foregoing, I would be really reluctant to use a couple of gull wing radials and call it good. Wes N7WS On 7/25/2019 12:37 PM, Richard (Rick) Karlquist wrote: On 7/25/2019 12:01 PM, Wes wrote: As to gull wing radials, Rudy Severns has looked at these too: https://www.antennasbyn6lf.com/files/antenna_ground_system_experiment_5.pdf Rudy's work is a treasure trove and I think I have everything he's written in a folder on my hard drive. Believe me, considering how difficult it is to lay radials in my cactus patch, if I thought gull wings would be useful I would have used them. I don't. Rudy shows gull wing down only 0.65 dB and comments that "radically changing the radial geometry does not seem to have a major impact". So I don't understand your remark that gull wings are not useful. The reduction in drive impedance can be mitigated by increasing the height by about 3 feet. I don't even have cactus but would never again run radials on the ground now that Rudy has educated us. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FCP vs Gull Wing Elevated Radials
Hi Wes, I have also always had the highest regard for 99.9% of anything that W8JI has stated. However, I feel exactly the same way about K2AV (and, of course, Rudy too). In this particular case, I am inclined to listen to Guy and the others here who have discussed and used the FCP. Probably, the FCP is a little inferior to either lots of radials or a few (two or more) elevated radials (like I have, which I assume is what is meant by "gull wings"). But for those who do not have the room for the said radials, K2AV's FCP is ab-so-lute-ly the way to go, isn't it? Not to pick on Tom, but he posted his page about silicone dielectric grease as a rebuttal to what I said about it, based on my particular experience with the brand of grease I used at the time. That and his article about the FCP are the only two times that I disagreed with him. :-) I was very lucky indeed to have him as one of my elmers. 73, Mike www.w0btu.com On Thu, Jul 25, 2019 at 2:01 PM Wes wrote: > Personally, I would and do, avoid a FCP antenna. W8JI has done some > analysis on > these and I value his insight. > http://www.w8ji.com/fcp_folded_counterpoise_system.htm There is simply > too much > handwaving going on to suit me. > > As to gull wing radials, Rudy Severns has looked at these too: > https://www.antennasbyn6lf.com/files/antenna_ground_system_experiment_5.pdf > Rudy's work is a treasure trove and I think I have everything he's written > in a > folder on my hard drive. Believe me, considering how difficult it is to > lay > radials in my cactus patch, if I thought gull wings would be useful I > would have > used them. I don't. > > Based on these and other resources, personal modeling and experiment and > physical constraints, I opted for a ground-mounted 55' vertical, > Inverted-L fed > against 18 (so far) 55' insulated, on-the-ground radials. By serendipity > the > radials are resonant at about 1.85 MHz although that was not a design > goal. > Instead, I chose radial length be the same as the vertical height and I > could > get nine, 55' radials out of a 500' spool of wire with negligible waste. > > Wes N7WS > > On 7/25/2019 10:04 AM, Mark K3MSB wrote: > > This kind of goes with the other thread that has morphed into the FCP > > topic, but is a bit different. > > > > With an FCP feeding the INV-L, the bottom of the INV-L will be at least > 10 > > feet off the ground.With my existing trees I can barely get up 50 > feet > > from the ground. So, the INV-L will have 40 feet of vertical radiator. > > > > Using a pair of resonant gull winged radials feeding the INV-L at the > > base, the vertical part will be 50 feet. > > > > From what I’ve read, the FCP is a better solution over a pair of > resonant > > gull wing radials, but I’ve also read that vertical length of an INV-L > is > > important. So there’s a tradeoff to be considered. > > > > Comments? > > > > Due to real estate considerations, I can put up only 2 one-half > wavelength > > resonant radials > > > > Mark K3MSB > > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FCP vs Gull Wing Elevated Radials
On 7/25/2019 12:01 PM, Wes wrote: As to gull wing radials, Rudy Severns has looked at these too: https://www.antennasbyn6lf.com/files/antenna_ground_system_experiment_5.pdf Rudy's work is a treasure trove and I think I have everything he's written in a folder on my hard drive. Believe me, considering how difficult it is to lay radials in my cactus patch, if I thought gull wings would be useful I would have used them. I don't. Rudy shows gull wing down only 0.65 dB and comments that "radically changing the radial geometry does not seem to have a major impact". So I don't understand your remark that gull wings are not useful. The reduction in drive impedance can be mitigated by increasing the height by about 3 feet. I don't even have cactus but would never again run radials on the ground now that Rudy has educated us. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FCP vs Gull Wing Elevated Radials
Personally, I would and do, avoid a FCP antenna. W8JI has done some analysis on these and I value his insight. http://www.w8ji.com/fcp_folded_counterpoise_system.htm There is simply too much handwaving going on to suit me. As to gull wing radials, Rudy Severns has looked at these too: https://www.antennasbyn6lf.com/files/antenna_ground_system_experiment_5.pdf Rudy's work is a treasure trove and I think I have everything he's written in a folder on my hard drive. Believe me, considering how difficult it is to lay radials in my cactus patch, if I thought gull wings would be useful I would have used them. I don't. Based on these and other resources, personal modeling and experiment and physical constraints, I opted for a ground-mounted 55' vertical, Inverted-L fed against 18 (so far) 55' insulated, on-the-ground radials. By serendipity the radials are resonant at about 1.85 MHz although that was not a design goal. Instead, I chose radial length be the same as the vertical height and I could get nine, 55' radials out of a 500' spool of wire with negligible waste. Wes N7WS On 7/25/2019 10:04 AM, Mark K3MSB wrote: This kind of goes with the other thread that has morphed into the FCP topic, but is a bit different. With an FCP feeding the INV-L, the bottom of the INV-L will be at least 10 feet off the ground.With my existing trees I can barely get up 50 feet from the ground. So, the INV-L will have 40 feet of vertical radiator. Using a pair of resonant gull winged radials feeding the INV-L at the base, the vertical part will be 50 feet. From what I’ve read, the FCP is a better solution over a pair of resonant gull wing radials, but I’ve also read that vertical length of an INV-L is important. So there’s a tradeoff to be considered. Comments? Due to real estate considerations, I can put up only 2 one-half wavelength resonant radials Mark K3MSB _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FCP vs Gull Wing Elevated Radials
Hi Mark, I suspect the current -- and hence the radiation -- from the bottom of the vertical radiator is somewhat suppressed by proximity to gull wing radials. When I first installed a 160 vertical using two gull-wing resonant radials eight feet high I had to increase height of the vertical radiator to achieve resonance at 1830 kHz. I had to shorten the radiator to the classic length w hen I later replaced the gull wing radials with sixty 120 foot radials laid on the ground. A little work in EZNEC would shed some light on this. 73 Frank W3LPL - Original Message - From: "Mark K3MSB" To: "topBand List" Sent: Thursday, July 25, 2019 5:04:33 PM Subject: Topband: FCP vs Gull Wing Elevated Radials This kind of goes with the other thread that has morphed into the FCP topic, but is a bit different. With an FCP feeding the INV-L, the bottom of the INV-L will be at least 10 feet off the ground. With my existing trees I can barely get up 50 feet from the ground. So, the INV-L will have 40 feet of vertical radiator. Using a pair of resonant gull winged radials feeding the INV-L at the base, the vertical part will be 50 feet. From what I’ve read, the FCP is a better solution over a pair of resonant gull wing radials, but I’ve also read that vertical length of an INV-L is important. So there’s a tradeoff to be considered. Comments? Due to real estate considerations, I can put up only 2 one-half wavelength resonant radials Mark K3MSB _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
